System and method for restricting access to a mobile communications network

ABSTRACT

There is described a system for restricting access to a mobile communications network for mobile communication devices within a restricted area. The system comprises at least one transmitter operable to transmit a beacon signal for reception by mobile communication devices within the restricted area and an access control entity, communicable with the mobile communication device via a base station. The access control entity instructs a mobile communication device to perform at least one measurement in regard of the beacon signal from each transmitter and then to provide measurement data corresponding to said performed measurement to the access control entity. The access control entity then analyses the measurement data provided by the mobile communication device and based on that analysis decides whether or not to provide the mobile communication device with access to a service of the mobile communications network.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/295,859, filed Mar. 7, 2019, which is a continuation of InternationalApplication No. PCT/GB2017/052657, filed Sep. 11, 2017, which claimspriority to UK Application No. GB1615372.8, filed Sep. 9, 2016, under 35U.S.C. § 119(a). Each of the above-referenced patent applications isincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to restricting access to a mobilecommunications network, and has particular relevance to a method inwhich access to the mobile communications network is restricted formobile communication devices within a particular location.

Description of the Related Technology

Mobile communications networks are becoming more and more ubiquitous.There are, however, some locations in which it is desired that access toa mobile communications network be restricted. One example of such alocation is the immigration area in an airport. Another example of sucha location is a courthouse or an embassy. Further examples of such areasare lecture halls, schools, cinemas and correctional institutions.

Various systems are already known for restricting access to a mobilecommunications network within a particular location. Such systems aretypically referred to as Managed Access Systems (MAS's). In some ofthese systems, access to the mobile communications network can bepermitted for certain mobile communication devices (such as cellularphones, also known as mobile phones and handy phones), identified forexample by the IMSI associated with the mobile communications deviceappearing on an “allowed” list, but restricted for mobile phones whoseIMSI does not appear on the “allowed” list. In this way, for example,passport officers within an immigration area of an airport may be ableto use their mobile communications devices while arriving passengerspassing through immigration are not able to do so.

A problem with such a system is that the restricted location is notwell-defined, and can extend to areas in which there is no reason whythe use of mobile communication devices need be restricted.

SUMMARY

According to a first aspect of the present invention, there is provideda system for restricting access to a mobile communications network formobile communication devices within a restricted area. The systemcomprises at least one transmitter operable to transmit a beacon signalfor reception by mobile communication devices within the restricted areaand an access control entity, communicable with the mobile communicationdevice via a base station. The access control entity instructs a mobilecommunication device to perform at least one measurement in regard ofthe beacon signal from each transmitter and then to provide measurementdata corresponding to said performed measurement to the access controlentity. The access control entity then analyses the measurement dataprovided by the mobile communication device and based on that analysisdecides whether or not to provide the mobile communication device withaccess to a service of the mobile communications network.

The beacon signal transmitters need have no other functionality. Inparticular, they need not have any capability to process a wirelesssignal from the mobile communication device, or to transmit any signalother than the beacon signal to the mobile communication device.Further, the beacon signal transmitters do not need to betime-synchronised or networked. Accordingly, the beacon signaltransmitters can be simple, inexpensive devices in comparison with abase station of a mobile communications network, and straightforward toinstall.

The beacon signal transmitters can be deployed around the perimeter of arestricted area or throughout a restricted area.

In an example, low-power beacon signal transmitters may be provided inan area in which access to a service provided by the mobilecommunications network is to be restricted. The power level of thelow-power beacon signal transmitters may be, for example, 0 dBm (i.e.1mW). In this example, if the measurement data indicates the presence ofa beacon signal transmitter, the access control entity restricts accessto the mobile communications network.

In another example, as well as the low-power beacon signal transmittersin an area in which access to a service provided by the mobilecommunications network is to be restricted, further low-power beacontransmitters can be provided in neighbouring areas. In this example, ifthe measurement data indicates the presence of a beacon signaltransmitter within the restricted area and the presence of a beaconsignal transmitter in a neighbouring area, then the access controlentity can decide to allow access to the mobile communications network.The decision to allow access may be performed based on a comparison ofthe measurement data for beacon signal transmitters within therestricted area and beacon signal transmitters outside of the restrictedarea.

In another example, beacon signal transmitters are provided outside of arestricted area but not inside the restricted area. The access controlentity can decide to restrict access for mobile communication devicescommunicating with a subject base station unless the measurement dataindicates the presence of a beacon signal transmitter. Such anarrangement may be advantageous if the restricted area is a substantialportion of the coverage area of the subject base station, or if it isdesirable not to deploy beacon signal transmitters within the restrictedarea.

In a further example, beacon signal transmitters may be deployed arounda restricted area with directional antennas arranged to direct thebeacon signal into the restricted area. Such beacon signal transmittersmay have a power of as much as 37 dBm (5W). In this way, whether or nota mobile communication device is within the restricted area can bedetermined based on the measurements of beacon signals transmitted bythe beacon signal transmitters, and accordingly the access controlentity can decide whether to restrict access based on the measurementdata from the mobile communication device.

The base station via which the access control entity communicates withthe mobile communication device may be a base station of the mobilecommunications network. If this is the case, then the mobilecommunications network may provide, via that base station, details ofthe beacon signal transmitters to the mobile communication device tofacilitate measurements of the beacon signals.

Alternatively, the base station via which the access control entitycommunicates with the mobile communication device may be a base stationof an independent mobile communications network. If this is the case,then neighbouring base stations from one or more public land mobilenetworks may provide details of that base station to the mobilecommunication device to facilitate handover to that base station. Suchan independent mobile communications network may permit signalling toother mobile communication networks via a network gateway.

Further features and advantages of the invention will become apparentfrom the following description of examples of the invention, which ismade with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a first example of an implementation of thepresent invention;

FIG. 2 schematically shows a second example of an implementation of thepresent invention;

FIG. 3 schematically shows a third example of an implementation of thepresent invention; and

FIG. 4 shows a schematic plan view of an implementation of the presentinvention in the immigration hall of an airport.

DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS

FIG. 1 schematically shows a system for controlling access of a mobilecommunication device 1 within a restricted area 3 (represented by thedashed block) to a mobile communications network. An example ofrestricted area 3 may be an immigration hall at an airport. In thisexample, the mobile communications network conforms to the GSMstandards.

As shown in FIG. 1, a plurality of measurement beacons 5 a-5 j aredisposed within the restricted area. A measurement beacon 5 is atransmitter that transmits a beacon signal. In this example, eachmeasurement beacon 5 is effectively a downlink only base station (BTS),which provides enough information (it is recommended a full BCCH withcell barring enabled, although a lesser subset (ie: FB/SB includingBSIC) could work) for the mobile communication device 1 to measure itsbeacon signal and report the measurement to the mobile communicationsnetwork for determination of action (ordinarily this would be ahandover).

The measurement beacons 5 are programmed in a way to make them uniquelyidentifiable within a code set and can be of varying power depending onthe desired area of coverage. Due to this ability to uniquely code eachbeacon it is possible to have many in a small area and identify each onefrom which a beacon signal is received, giving the benefit of providingcoarse positional information.

The mobile communication device 1 communicates with base stations 7 a-7c of a public land mobile network (PLMN). In FIG. 1, two of the basestations 7 a, 7 b are connected to a first base station controller 9 awhile the other base station is connected to a second base stationcontroller 9 b. The first and second base station controllers 9 a, 9 bare connected to a mobile switching centre 11, which is in turnconnected to a Visitor Location Register (VLR) 13 and a gateway 15.

GSM and other cellular protocols provide for a list of neighbour cellsto be advertised from a serving base station. In the case of GSM, thisis advertised in the System Information 5 message, carried on adedicated channel during a communication session between a MS and a BTS.ETSI specification GSM04.08 section 9.1.3.7 clearly describes theprocess for encoding an SI5 message, and section 3.4.1 describes when itshould be present.

When a dedicated channel is established, an MS will attempt to measureall the cells which are handover candidates from the SI5 message andreturn these values to the serving BTS in a Measurement Report. Thisprocess is described in GSM04.08 section 3.4.1.2, and GSM05.08, section8. The pertinent features for this invention are the recovery ofARFCN/RXLEV/RXQUAL and B SIC.

In this example, the operator of the PLMN has allowed the airport to usea block of ten GSM channels to facilitate operation of the invention—adescription of each measurement beacon's configuration is illustratedbelow:

Location BCCH BSIC Beacon 5a 870 1 Beacon 5b 872 2 Beacon 5c 874 3Beacon 5d 876 4 Beacon 5e 878 5 Beacon 5f 871 6 Beacon 5g 873 7 Beacon5h 875 9 Beacon 5i 877 10 Beacon 5j 879 11

This configuration takes into account the properties of channelseparation for GSM to work effectively, and the measurement beacons 5would be of a low power, for instance 0 dBm. Mobile network technologyhas been designed to allow for determination of multiple cells or atleast the dominant cell in an environment where more than one cell canbe received on a single ARFCN. In GSM, this is the function of the BSIC.It is required that the network operator puts the list of ARFCN's forthe beacons into an SI5 list of its local BTS's that service theairport.

When the user of the mobile communication device 1 attempts to performany type of activity, for instance making a call, sending an SMS orstarting a data session, a dedicated channel is established between themobile communication device 1 and the serving base station 7. This willtrigger the sending of the Measurement Reports to the BSC 9, and thesewill contain measurements received from cells contained in the SI5message. It would also be completely normal for this SI5 list to containthe adjacent cells of the network as well as the artificially introducedbeacons as the network will still use the non-beacon channels forhandover. The standards dictate that at least the top six strongestmeasured cells must be reported where they can be decoded.

Once a dedicated channel is established, it can be calculated quickly ifthe user of the MS is in the vicinity of the measurement beacons 5 inthe restricted area 3 due to the presence or lack of ARFCN/BSICcombinations deployed at the airport in the measurement reports that theMS will be sending. The RXLEV and RXQUAL will also give a determinationof how close the MS is to the beacon.

If there are no measurements received with the ARFCN/BSC combinationfrom the airport then it can be assumed that the MS is not present inthe restricted area 5 and therefore the mobile communication device 1can be given full network access. If however any of the ARFCN/BSICcombinations from the restricted area are received in the measurementreports then it can be deduced that the mobile communications device 1is in the vicinity of one or more of the measurement beacons 5.Additionally, it is possible to identify an approximate location of themobile communications device 1 based on the RXLEV for the reportedmeasurement beacons 5. For instance:

BCCH BSIC RXLEV 874 3 38 876 4 35 878 5 54 871 6 55

In the example above, we could deduce that the MS is positioned betweenmeasurement beacons 5 e and 5 f due to the similar RXLEV's from thosemeasurement beacons 5. Analytical software can be used to determine theposition of the MS based on the RXLEV's from the MS. Such analyticalsoftware typically requires some of the following inputs to estimate amobile's position in a MAS system:

-   -   1) Details of beacon placement, transmit power, antenna facing,        channel number and BSIC.    -   2) RF propagation models based on the above when combined with        structural models of the site or facility of interest, including        such things as placement and materials for walls, ceilings and        floors, ducting and any other significant metallic bodies.    -   3) RF survey results from walk test of the facility or sites of        interest.        Given one or more measurement reports from a mobile, the        analytical software can compare the top 6 reported neighbour        BSIC and RXLEV values to models formed from the above data to        produce estimates as to the likely location or locations of an        MS. Collecting successive measurement reports can allow for        further accuracy in the positioning estimate by further        processing the reported RXLEV values to remove the effect of RF        fading by filtering or averaging.

The base stations for the restricted area are configured such that theirBA lists for dedicated mode (the SI5 set of messages) include the radiochannels (ARFCNs) used by the beacons in the system. An additionalmodification may also be made to the BTS operation such that dedicatedchannels are held connected for a minimum amount of time sufficient for:

1) A MS to detect and measure a neighbour cell, or beacon in this case

2) The MS to report the top 6 cells to the BTS in a Measurement Reportmessages

The 3GPP standards define the Measurement Reporting period as 480ms, andalso set requirements on neighbour cell detection and measurementfrequency and accuracy. The maximum duration of a dedicated channel issubject to protocol stack guard timers and cannot be indefinite withoutsignalling progress being made, but can be extended towards 10 secondswithout problem. The dedicated channel can be held open for a variableduration to allow collection of more or fewer Measurement Reports asrequired to achieve the required confidence in the analytical result.This may also use prior decisions such that MS's which have already beenfound to either be within or outside the area of effect are quicklyhandled without holding resources at the base station for longer thannecessary.

The decision making process would be coded in an ordinary network in theMSC 11 in the form of an access control entity, via extensions from theBase Station Controller to forward the measurements as ordinarily theMSC 11 is not aware of radio measurements. To a person skilled in theart, there are several ways to achieve this including proprietary orstandards compliant messaging, and it would even be possible to processthe measurement reports from a mobile communication device 1 todetermine if it is in the restricted area 3 inside the BSC 9, and simplypass a decision message to the MSC 11.

So far as the MSC 11 is concerned, one possible method to implement theaccess control entity could be an additional step in the MMLocation/Routing Update procedure which would follow the identity andoptional authentication responses. Once the mobile communications devicehas been determined to be allowed onto the network through a HLR check,a further step would take place to validate the measurement reports anddetermine if the mobile communications device 1 is in the restrictedarea 3. If the mobile communications device 1 is not in the restrictedarea 3 then the regular process would be followed, however, if themobile communications device is in the restricted area 3 then a suitablelayer three response could be issued to the mobile communication device1 such as “congestion”. This would cause the mobile communication device1 to frequently retry, thus allowing an immediate reversion back toregular service once out of the restricted area 3.

In another example, the access control entity could be coded into theMSC 11 to extend the process CM Service Request procedures for SMS andCalls. When the mobile communications device 1 initiates a call, a CMService Request message is sent to the base station 7. At this time theMSC 11 could wait for a set of measurement reports and determine if themobile communications device 1 is in the restricted area 3. If not, thenthe normal procedure could be followed, otherwise a suitable layer threerejection message could be passed back to the MS such as “Congestion”.

In yet another example, the access control entity could be coded purelyinto the MSC 11 provided that the BSC 9 was configured so that theBeacon ARFCN/BSIC values were treated as an inter-MSC cell list. Thiswould not provide the complete set of measurements to the MSC 11,however, it would be a simpler implementation as the BSC 9 if correctlyconfigured, would tell the MSC that it needed to perform an inter-MSChandover to one of the Beacons. At this point, the MSC, knowing that thehandover candidate is not an actual base station 7 would simply teardown the session with a layer three Channel Release message. This methodhas the advantage of being able to stop a session which was establishedprior to a mobile communication device 1 entering into the restrictedarea 3.

Ideally, all three examples above could be implemented in parallel. Thisway you can restrict access at authentication level, setup attempt, andcease traffic that is already established. For data sessions the sameprocess could be applied at the SGSN, or even in the IP domain providedthat you could tie the IP session to an IMSI/IMEI in the restrictedarea.

In the above examples, the access control entity is implemented by anetwork operator after integrating associated code into their corenetwork or radio access network or distributed between the core networkand the radio access network. In alternative examples, an independentbase station (that is one not forming part of the main Public LandMobile Networks) is introduced into the network. As shown in FIG. 2, theindependent base station 23 may be connected to an independent BSC 25and an independent MSC 27. The MSC 27 may be connected to a gatewaydevice (not shown) allowing communication with PLMNs.

The independent base station 21 has a coverage area extending over, butnot necessarily limited to, the restricted area. The independent basestation 21 has a different Location Area Code to the surrounding networkand therefore triggers a Location Update procedure to any mobilecommunication device which comes into range of it. At this point, themeasurement of the beacon signals from the measurement beacons 5 can betriggered, the resultant measurement data analysed and the appropriatelayer three response issued to the MS. The benefit of the forcedLocation Update procedure is the ability to control the MS atauthentication point and make it indicate “NO SERVICE” if necessary. Abenefit of this approach is that it does not require any changes to thenetwork operator's infrastructure outside the building, although it maybe advantageous for neighbouring base stations preferentially tohandover mobile communication devices to the independent base station.

As shown in FIG. 3, in another example instead of positioningmeasurement beacons within the restricted area 5, measurement beacons 31with directional antennae can be provided around the periphery of therestricted area 5. The directional antenna for each measurement beacon31 directs the associated beacon signal to the restricted area 5, andthe measurement beacons 31 are arranged so that whether or not themobile communication device 1 is within the restricted area 3 can bedetermined from measurements of the beacon signals.

One of the key advantages of this invention is the ability to tightlycontrol a perimeter. For instance, FIG. 4 schematically shows for theimmigration are example previously mentioned, an immigration hallbounded by walls 41 b and 41 c, with a departures lane passing nearbybetween walls 41 a and 41 b. The immigration line, guided by barriers 43a-43 c, directs people to passport check booths 45 a-45 h, each passportcheck booth 45 holding two passport check positions. In this example,measurement beacons 5 a-5 h (hereafter referred to as deny measurementbeacons) are provided adjacent the passport check booths 45 andmeasurement beacons 5 i-5 k (hereafter called override measurementbeacons) are provided in the departure lane. The deny measurementbeacons and the override measurement beacons are functionally identical,but the access control entity treats them differently. For example, theaccess control entity could apply an algorithm such as: Deny Access ifany three ARFCN/BSIC combinations for deny measurement beacons haveRXLEV>30, unless an ARFCN/B SIC for an override measurement beacon hasan RXLEV>30, in which case allow access—this is of course possible dueto the ability to uniquely identify each Beacon. Once the Beacons areinstalled, it would be relatively straightforward to analyse themeasurements and in fact, using measurement tools at installation theradio environment could be modelled to provide detailed positioningdata.

In an alternative example, no deny measurement beacons are needed butonly override measurement beacons are provided, detection of one or moreoverride measurement beacons overriding a default decision to denyaccess.

In an example, successive measurement reports may give different sets ofBSICs and RXLEV values, indicating that the MS is in motion. Using priorknowledge of beacon placement, the speed of the MS can be estimated. Initself for some sites this may provide evidence that an MS is forexample, moving by car down a road adjacent to the desired restrictedarea, as opposed to being within the restricted area presuming thatthere are no parallel roads on site.

The description herein describes this technology being used in a GSMnetwork, however, the person skilled in the art will know that it can beapplied to other Radio Access Technologies (RATs). For instance to usethis method in UMTS, the Beacon would have a distinct UARFCN/PSCcombination, and in LTE it would have a distinct EARFCN/PCI combination.Additionally it is possible in more modern RATs to prioritise certaincells using hierarchy such as HCS. This allows the Beacons to bemeasured first if necessary. It is also possible in higher technologyRATs to force an MS to measure a lower technology RAT cell, thus itwould be possible to use GSM beacons in an LTE or UMTS network undermost circumstances.

What is claimed is:
 1. A system for restricting access to a mobilecommunications network by mobile communication devices within arestricted area, the system comprising: a plurality of transmitters eachconfigured to transmit a respective beacon signal for reception by themobile communication devices within the restricted area; and an accesscontrol entity, communicable with a mobile communication device via abase station, wherein: the access control entity is configured todecide, based on measurement data from the mobile communication deviceindicative of reception by the mobile communications device of thebeacon signals transmitted by the plurality of transmitters, whether ornot to provide the mobile communication device with access to a serviceof the mobile communications network.
 2. A system according to claim 1,wherein each transmitter is arranged so that the beacon signal emulatesa signal emitted by a base station of a mobile communications network toindicate the presence of that base station.
 3. A system according toclaim 1, wherein each of the plurality of transmitters is a simplexcommunication device.
 4. A system according to claim 1, wherein each ofthe plurality of transmitters transmits the beacon signal at a power ofabout 0 dBm.
 5. A system according to claim 1, wherein each of theplurality of transmitters comprises a directional antenna.
 6. A systemaccording to claim 1, wherein the access control entity is arranged todeny access to the service of the mobile communications network underone or more conditions, the one or more conditions including if themeasurement data indicates that at least one detected beacon signalsatisfies a measurement condition.
 7. A system according to claim 1,wherein the access control entity is arranged to allow access to theservice of the mobile communications network under one or moreconditions, the one or more conditions including if the measurement dataindicates that at least one detected beacon signal satisfies ameasurement condition.
 8. A system according to claim 1, wherein theaccess control entity is arranged to vary a time for which a dedicatedchannel with a mobile communications device is held open, wherebyenabling a varying number of measurement reports to be received from themobile communications device.
 9. A system according to claim 1, whereinthe access control entity is provided in the mobile communicationsnetwork.
 10. A system according to claim 9, wherein the access controlentity is implemented by code in a radio access network, a core network,or both the radio access network and the core network of the mobilecommunications network.
 11. A system according to claim 1, wherein: themobile communications network is a first mobile communications network;the access control entity is arranged to control access to the serviceprovided by the first mobile communication network, and the accesscontrol entity is provided in a second mobile communication networkseparate from the first mobile communication network.
 12. A systemaccording to claim 1, wherein said service is a voice call, an SMSmessage or a data session.
 13. A system according to claim 1, whereinthe measurement data is provided in a measurement report in accordancewith a wireless communications standard.
 14. A system according to claim13, wherein the wireless communications standard is the GSM standard.15. A system according to claim 1, wherein the access control entity isconfigured to transmit a layer three message to the mobilecommunications device via the base station upon deciding not to providethe mobile communication device with access to the service of the mobilecommunications network, the layer three message being a rejectionmessage or a channel release message.
 16. A system according to claim15, wherein the layer three message is a rejection message indicatingcongestion.
 17. A method of restricting access to a mobilecommunications network by mobile communication devices within arestricted area, the method comprising: providing a plurality oftransmitters each configured to transmit a beacon signal for receptionby the mobile communication devices within the restricted area;receiving a measurement report from the mobile communications device,the measurement report conveying measurement data indicative ofreception by the mobile communications device of the beacon signalstransmitted by the plurality of transmitters; and deciding, based on themeasurement data from the mobile communication device, whether or not toprovide the mobile communication device with access to a service of themobile communications network.
 18. A method according to claim 17,wherein at least one of the plurality of transmitters is disposed withinthe restricted area.
 19. A method according to claim 17, wherein atleast one of the plurality of transmitters is disposed outside of therestricted area and has a directional antenna that directs the beaconsignal transmitted by that transmitter into the restricted area.
 20. Amethod according to claim 17, wherein the restricted area comprises animmigration hall of an airport.